Pure nitride materials such as, for example, AlN and Si.sub.3 N.sub.4, are very difficult to sinter into bodies of near theoretical density from high purity powders because of the extremely low self-diffusion rates in those strongly covalently-bonded materials. Thus, temperatures of 1800.degree. C. and higher have been required to achieve bodies of nearly full density.
This invention is directed to means for producing highly refractory, sintered bodies of nitride materials exhibiting nearly theoretical density and excellent mechanical strength wherein the temperatures needed for sintering can be relatively low. Most particularly, this invention is concerned with means for preparing sintered bodies of AlN demonstrating nearly full density and exceptional thermal conductivity.
Aluminum nitride (AlN) has recently gained considerable attention for its proposed application as a substrate or heat sink in integrated circuit packages due to its potentially high thermal conductivity together with a high electrical resistivity (at least 10.sup.11 ohm cm up to in excess of 10.sup.15 ohm cm), a dielectric constant of about 9-10, and a coefficient of thermal expansion close to that of silicon. Although AlN has been predicted to have a thermal conductivity of 320 W/m.K, most polycrystalline AlN ceramic bodies known in the literature have manifested a thermal conductivity over the interval of about 35-70 W/m.K.
The primary objective of the instant invention is to produce highly refractory, sintered bodies of nitride materials of near theoretical density by firing at temperatures as low as 1400.degree. C. with or without externally applied pressure. A more specific second objective of the invention is to prepare highly refractory, sintered AlN-based ceramic bodies of nearly full density and much enhanced thermal conductivity relative to AlN bodies produced in the conventional manner.